Microstrip transmission line with a high permeability dielectric



July 12, 1966 G. PUSCH 3,260,972

MIQROSTRIP TRANSMISSION LINE WITH A HIGH PERMEABILITY DIELECTRIC Filed June 11, 1962 fm/emon' e UNT ER P USCH BY: W

ATTQRNE Y conductor plate.

United States Patent 3,260,972 MICROSTRIP TRANSMISSION LINE WITH A HIGH PERMEABILITY DIELECTRIC Giinter Pusch, Hanover, Germany, assignor to Telefunken Patentverwertungs-G.m.b.H., Ulm (Danube),

Germany Filed June 11, 1962, Ser. No. 201,597 Claims priority, application Germany, June 7, 1961,

3 Claims. 61. 333-84) The present invention relates generally to circuit devices, and, more particularly, to such devices of the type wherein conductors are mounted on an insulating layer.

Conductor circuits or resonant lines have been provided in the past in the form of two printed conductor trains or transit paths which extend side by side on a printed However, such conductor circuits can only be used with relatively high frequencies since their dimensions would be too large when they are designed for use in the lower frequencies.

In order to reduce these large dimensions, the conductors of high frequency transformers with a line in the form of a spiral or coil have been provided in the past. However, the amount of space which is required even in this construction is still so great that the frequency range in which these conductors are used as a practical matter can be extended into the lower frequencies only to a limited extent.

With these defects of the prior art in mind, it is a main object of the present invention to provide a circuit device of the character described wherein the frequency range in which these conductor circuits may be used can be extended downwardly into the lower frequencies to a substantial extent.

Another object of the invention is to provide a conductor circuit device which may easily be constructed intoany desired space-saving shape.

A further object of the invention is to provide conductor circuits of the character described wherein band pass filters may be produced in a simple manner.

Still a further object of the invention is to provide a device wherein two conductor pairs may be provided and the coupling therebetween may be of any desired type which may be regulated by the accurate spacing of the mutual distance between the two conductor pairs.

Still another object of the invention is to provide a device wherein the electrical length of the conductor device may be increased by suitable construction.

These objects and other ancillary thereto are accomplished according to preferred embodiments of the invention wherein a conductor circuit is provided which includes conductors mounted upon a layer of insulating material. The conductors are so arranged that they are mounted on opposite sides of the layer of insulating material and positioned opposite each other. They preferably are in the form of thin strips. Also, the insulating material at least partially comp-rises a material of a high permeability. Due to this insulating layer between the conductors, the distributed inductance and the distributed capacity are strongly increased with a given geometric dimension, and the electrical length of the line is also increased. It is also possible to terminate the line in its characteristic impedance and then the line may be used, for example, as a delay line. The insulating material of high permeability used according to the invention is the so-called ferrite known in the art.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a diagrammatic perspective view of an "ice embodiment of the instant invention wherein the conductors are totally surrounded by the insulating material.

FIGURE 2 is a diagrammatic side elevational view of a device similar to that of FIGURE 1, but in coiled form.

If a layer of insulating material is provided as a flexible strip, the line and thus the conductor circuit thereby formed may be arranged into any desired shape. For example, the strip with the conductors may be coiled and an intermediate layer of insulating material used to in sulate and decouple the individual couplings or coils from one another, and this type of conductor circuit will occupy the smallest possible amount of space.

Band pass filters may be produced by mounting at least two pairs of oppositely positioned conductors on the insulating material layer, with the pairs disposed side by side and so positioned from one another that the two conductor circuits thereby formed are coupled with each other. This coupling may be regulated by .a suitable spacing of the mutual distance between the two conductor pairs. An inductive coupling, a capacitative coupling and a galvanic coupling, are all possible couplings which may be provided between the circuits. To provide the galvanic coupling, galvanic cross connections are used between the conductor circuits, and this may take the form of a conductor of the same type of material as the others, which directly connects the two conductor circuits.

If several conductor circuits are mounted side by side on the layer of insulating material, the conductors on one side of the layer may be combined into a broad metal strip or band which then may serve as a ground wire. The other conductors on the opposite side of the layer may each respectively comprise, together with the metal strip, a separate line.

When the layer of insulating material is in the form of a rigid plate or the like, it is particularly expedient to mount the two oppositely positioned conductors on the insulating layer in meandering fashion in order to save space. The insulating material will be in the form of a plate if it is formed wholly of ferrites which, as is well known, possess insulating properties.

In order to provide tuning conductor circuits, pieces of powdered iron or some other type of high frequency or radio frequency iron may be fastened to the conductors in a suitable manner, for example by gluing. The tuning is then provided by changing the amount of overlap between the piece or pieces of iron and the conductors. Tuning may also be provided by changing the length or the width of the conductors.

Band pass filters may be formed by using several pairs of conductors and mounting them on the layers of insulating material in meandering fashion and using inductive, capacitative, or galvanic couplings. When an inductive coupling is to be used, sections of the pairs of the conductors are disposed parallel to each other, and for galvanic couplings direct electrical connections are provided between the conductors.

The electrical length of a conductor circuit with given geometric dimensions may be increased even further if the layer of insulating material is constructed of a material having a high dielectric constant at the places where high voltage will occur. In such an embodiment the insulating material is a material provided with a high permeability between the conductors at the places where high current peaks occur, and is constructed of a material having a high dielectric constant at those places where high voltage peaks occur.

In another embodiment of the invention, the electrical length is also increased by closing the magnetic circuits around the two conductors using additional layers of insulating material also of high permeability. These layers are mounted over the conductors and touch the insulating material layer on both sides of the conductors, so that the conductors are totally enveloped or surrounded thereby.

With more particular reference to the drawings, FIG- URE 1 shows a first embodiment of the invention. The layer of insulating material 1 has a high permeability and conductors 2 and 3 are mounted on the layer 1, each on a different side thereof and are provided in the form of flat strips. In addition, layers of insulating material a and b are provided above and below the conductors 2 and 3. These layers completely close the magnetic circuit around conductors 2 and 3 and due to this the distributed induction of the conductor circuit is substantially increased and the electrical length correspondingly increases with any given geometric dimension. The layers a and b are constructed of a similar material as the layer of insulating material 1, or of any other insulating material which has a high permeability in order to close the magnetic circuit about the conductors.

In order to tune this type of conductor circuit, a slot or recess may be provided in one of the insulating material layers, which in this embodiment is indicated as layer a. The slot may extend transversely to conductor 2 to which it is adjacent. A strip 0. is inserted in the slot or recess for tuning purposes and this strip is also constructed of a material having high permeability so that its position in the recess or slot may be adjusted in order to provide for tuning. The embodiment of FIGURE 2 is similar to that of FIGURE 1. In this embodiment, conductors 7 and 8 are mounted on an insulating material layer 6, all of which are flexible, and they are covered by layers e and f of insulating material of high permeability and which project laterally of the conductors 7 and 8 and touch the insulating material layer 6 which also is of high permeability. Thus, the magnetic circuits surrounding conductors 7 and 8 are completely closed and the electrical length with any given geometrical dimension is thereby materially increased.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is: 1. A circuit device, comprising, in combination: (a) a layer of insulating material at least partially formed of a material having a high permeability; (b) two conductors mounted on said layer on opposite sides thereof and opposite each other; and (c) means for closing the magnetic circuits around the two conductors, said means including an additional layer of insulating material having a high permeability mounted on each of the conductors and engaging said first mentioned layer on both sides. 2. A device as defined in claim 1 wherein said layers and thus said conductors are coiled.

3. A device as defined in claim 1 wherein said layers and thus said conductors are fiat.

References Cited by the Examiner UNITED STATES PATENTS 2,411,555 11/1946 Rogers 333-84 2,537,959 1/1951 Beverly 33331 2,787,656 4/1957 Raisbeck 333-24 2,896,177 7/1959 Wilson 333-84 2,998,840 9/1961 Davis 33331 FOREIGN PATENTS 802,578 2/1951 Germany.

OTHER REFERENCES Cohn, M.: Propagation in Dielectric-Loaded Parallel Plane Waveguide, in IRE Transactions on Microwave Theory and Techniques, April 1951, vol. MTT7, No. 2, pages 202-208, page 205 relied on.

Jones: Thin Film Electronic Circuits, IBM Technical Disclosure Bulletin, vol. 3, No. 10, March 1961, page 101.

HERMAN IQARL SAALBACH, Primary Examiner.

S. D. SCHLOSSER, L. ALLAHUT, Assistant Examiners. 

1. A CIRCUIT DEVICE, COMPRISING, IN COMBINATION: (A) A LAYER OF INSULATING MATERIAL AT LEAST PARTIALLY FORMED OF A MATERIAL HAVING A HIGH PERMEABILITY; (B) TWO CONDUCTORS MOUNTED ON SAID LAYER ON OPPOSITE SIDES THEREOF AND OPPOSITE EACH OTHER; AND (C) MEANS FOR CLOSING THE MAGNETIC CIRCUITS AROUND THE TWO CONDUCTORS, SAID MEANS INCLUDING AN ADDITIONAL LAYER OF INSULATING MATERIAL HAVING A HIGH PERMEABILITY MOUNTED ON EACH OF THE CONDUCTORS AND ENGAGING SAID FIRST MENTIONED LAYER ON BOTH SIDES. 